Downhole geothermal production pumps are adapted to lift geothermal fluid from within a well or column to the ground surface. The geothermal fluid is pumped at a high temperature and pressure, e.g. a temperature in the order of 500° F. and a pressure in the order of 300 psi which is greater than its flash point, in order to ensure continual geothermal liquid flow throughout the geothermal system and thus also prevent scale precipitation.
Due to the high temperature and pressure of geothermal fluid, considerable pump bearing wear is noticeable. Petroleum oil is generally used as a lubricant, to prevent excessive wear to a bearing mounted on the main pump shaft. However, the drive shaft and bearings of geothermal production pumps are prone for failure as a result of the intrusion of the high-pressure geothermal fluid into the line through which the lubricant is delivered. Bearing failure is also caused by the precipitation of scale thereon.
U.S. Pat. No. 4,276,002 discloses a submerged turbopump unit for pumping hot geothermal liquids from deep wells to the earth's surface. The wear of the bearings associated with the turbopump is minimized by supplying lubricating liquid, e.g. hot water, thereto which is taken from an intermediate stage of a centrifugal pump at the surface which supplies motive liquid to the turbine.
However, no prior art water-lubricated bearings are known to the applicant for the long drive shaft (hereinafter referred to as a “line shaft”) extending from a surface mounted motor to the pump submersed in the water column. U.S. Pat. No. 4,276,002 describes an improved turbopump unit for pumping hot geothermal liquids from deep wells. However, there are many technical challenges of applying geothermal water to line shafts even when taking the teachings of U.S. Pat. No. 4,276,002 into consideration. These challenges include mechanically sealing the shaft at the surface, maintaining pressure above saturation in a low pressure system and, in addition, dealing with the corrosiveness of geothermal fluid to line shaft bearings. For example, it is recited in U.S. Pat. No. 4,276,002 that bled geothermal water needs to be cooled and filtered.
It is an object of the present invention to provide a geothermal production pump bearing which is unaffected by the intrusion of geothermal fluid into the lubrication line.
It is an additional object of the present invention to provide a reliable water lubricated line shaft bearing.
It is an additional object of the present invention to provide a water lubricated geothermal line shaft bearing which is unaffected by the precipitation of scale thereon during the flow of lubrication water.
It is yet an additional object of the present invention to provide a water lubricated geothermal line shaft bearing which has sufficient strength to withstand high compressive loads imposed by the rotating line shaft.
It is yet a further object of the present invention to provide a lubrication system that ensures sufficient lubrication of the line shaft bearing.
Other objects and advantages of the invention will become apparent as the description proceeds.